This invention relates to a protocol encoding/decoding device for use in syntax conversion or translation between an abstract syntax and a transfer syntax.
As is well known in the art, a layer protocol of Open Systems Interconnection (OSI) consists of seven layers which comprise a physical layer, a data link layer, a network layer, a transport layer, a session layer, a presentation layer, and an application layer.
Attention will be directed to the presentation layer and the Application layer. In the application layer, its layer protocol is described in an abstract by using an Abstract Syntax Notation One (ASN.1) which is defined in International Organization for Standardization (ISO) 8824 and the International Telegraph and Telephone Consultive Committee (CCITT) Recommendation X.208. The ASN.1 is a programming language for describing complicated data structure in the application layer. The ASN.1, which is similar to a normal programming language, is capable of describing the complicated data structure consisting of a combination of simple data types. A set of data types described by ASN.1 is called the abstract syntax. The abstract syntax is independent from its coding format in a real system. In the presentation layer, the abstract syntax is encoded into the transfer syntax on the basis of the ASN.1 basic encoding rules which are defined in ISO 8825 and CCITT Recommendation X.209. A function of the application layer is realized by a function module called an application entity while another function of the presentation layer is realized by another function module called a presentation entity. The application entity represents semantices of data by using the abstract syntax. The transfer syntax represents syntax of data transferred between the presentation entities. Each OSI presentation layer protocol is represented as a set of Protocol Data Units (PDUs) described by the transfer syntax. Each PDU includes a plurality of components.
In order to input/refer a data value as one of the components, it is necessary to recognize the complex data structure of the abstract syntax. For that purpose, in the prior art, structures and a Value Tree List (VTL) must manually be generated on the basis of the abstract syntax. The value tree list is a table indicative of a matching between the generated structures and data values for the data structure of the abstract syntax. In addition, complicated interface conversion between the value tree list and a user program must manually be carried out. It is therefore necessary to carry out individual processings for encoding/decoding of OSI Application layer protocols, respectively.
As a result, it is difficult for the prior art to carry out input/reference of a desired data value. In particular, in a case where the data structure of the abstract syntax is complicated, lack of information occurs due to mistakes about the input/reference of the data value, it is difficult to understand the data structure of the abstract syntax itself, and it is necessary to carry out a lot of processings corresponding to each OSI Application layer protocol.